The present invention is directed to an optical assembly for an exposure apparatus. More specifically, the present invention is directed to an optical assembly having ports strategically positioned for purging the optical assembly and a method for efficiently purging an optical assembly.
Exposure apparatuses are commonly used to transfer an image from a reticle onto a semiconductor wafer. A typical exposure apparatus includes an apparatus frame, an illumination source, a reticle stage, a wafer stage, and an optical assembly which cooperate to transfer an image of an integrated circuit from the reticle onto the wafer. The illumination source generates a beam of light energy which passes through the reticle. The optical assembly directs and/or focuses the light passing through the reticle to the wafer.
The size of the integrated circuits transferred onto the wafer are extremely small. Accordingly, the precise directing and/or focusing of the light by the optical assembly is critical to the manufacture of high density semiconductor wafers.
Unfortunately, depending upon the type of light generated by the illumination source, the type of fluid in the optical assembly can influence the performance of the exposure apparatus. For example, some types of light are absorbed by oxygen. As is well known, air is a gaseous mixture which is approximately twenty-one percent oxygen. Thus, air in the optical assembly can influence the performance of the optical assembly and the exposure apparatus. As a result thereof, the quality of the integrated circuits formed on the wafer can be compromised.
In light of the above, it is an object of the present invention to provide an exposure apparatus which is capable of generating high resolution patterns on a semiconductor wafer. Another object of the present invention to provide an optical assembly which can be purged of any unwanted fluid relatively easily and efficiently. Still, another object of the present invention is to provide an optical assembly which minimizes the amount of time required to dilute the unwanted fluid and the amount of replacement fluid used to dilute the unwanted fluid in the optical assembly to acceptable levels.
The present invention is directed to an optical assembly for directing and/or focusing a beam of light energy. The optical assembly includes an optical housing having an inner wall which defines an optical chamber. One or more optical elements are secured to the optical housing. Additionally, the optical assembly includes an outlet port and an inlet port for purging the optical chamber. Uniquely, the inlet port directs a replacement fluid from a fluid source into the optical chamber substantially tangential to the inner wall of the optical housing so that the replacement fluid swirls in a first rotational direction in the optical chamber. This minimizes the time needed to purge the optical assembly of any unwanted fluid and the amount of replacement fluid used to dilute the unwanted fluid in the optical chamber to acceptable levels.
Preferably, the optical housing includes a plurality of inlet ports and a plurality of outlet ports placed at various strategic locations around the circumference of the optical housing. The inlet ports are strategically positioned to maximize flow velocities and fluid mixing within the optical chamber. For example, upper inlet ports can be positioned near an upper region of the optical housing and lower inlet ports can be positioned near a lower region of the optical housing. These inlet ports circulate the fluid in a circular pattern in the optical chamber and direct the fluid towards an intermediate region of the optical housing.
The outlet ports are also designed to assist in creating and controlling the flow patterns of the fluid in the optical chamber. For example, outlet ports are positioned in the intermediate region of the optical housing to receive the fluid forced to the intermediate region. Additional outlet ports are positioned near each optical element to exhaust the fluid in the tight spaces near each optical element. These outlet ports reduce the amount of trapped gasses and reduce the amount of dilution time required to replace the unwanted fluid with the replacement fluid.
Additional inlet ports can be used to reverse the direction of the swirl within the optical chamber. With this design, the inlet ports may be pulsed on and off in both directions to create turbulence within the optical chamber. The turbulence improves mixing of the fluids in the optical chamber and reduces the amount of time required to dilute the unwanted fluid in the optical chamber.
The present invention is also a method for purging an optical housing of an optical assembly. The method includes the step of directing a fluid into the optical chamber substantially tangential to the inner wall so that the fluid swirls in a first rotation direction in the optical chamber.